Enter the LifeStraw Mission water purifier, a beefed up version of the popular LifeStraw personal water filter that is equally suitable for a zombie apocalypse bug-out bag or - much more likely - a small community stricken by drought or other disaster.

A quick primer: both purifiers and filters remove bacteria and protozoa, but only a purifier removes viruses, and to remove particulates like dirt, sand, etc. you may need to let it settle or pre-filter with your shirt or something similar. To clean water the gold standard is boiling for one minute, which nukes everything. But boiling is fuel dependent, not always an option, so then you basically have your choice of the chemical option (chlorine a.k.a. household bleach, or iodine tablets - both have advantages and disadvantages or brine), the ultraviolet light option (requires batteries and water that's not too cloudy), or mechanical methods that force water through a physical filter (hand pump, suction straw, or gravity feed). For more info check out REI's guides to backcountry and international water treatment.

So back to the LifeStraw Mission, a seriously cool under-a-pound solution that uses the last method, gravity feed, and is about as simple as it gets: fill the 5 or 12 liter BPA-free roll-top bag with water, hang it up, and let Sir Isaac Newton go to work for you. Repeat for 18,000 liters or 4,755 gallons, at a flow rate of up to about three gallons an hour of perfectly safe drinking water. There is no imparted taste, and the pre-filter works to get the big nasties out. They even include four extra pre-filters, a stuff sack and a shoulder strap.

The LifeStraw Mission was available exclusively through REI until July 1st, and it should make its way into other storefronts real soon now. Need more motivation? Vestergaard, the manufacturer of LifeStraw, uses a portion of its profits to distribute its products to needy communities: visit www.followtheliters.com to check out a great product for a great cause.